The current attenuator or filter includes three types, namely, active type, passive type and digital type. Passive filter is formed by resistor, capacitor and inductor. The passive filter must consider the quality factor of inductor and capacitor, but in CMOS process, the quality factor of the inductor is generally not good, which results in its bad performance. In the active filter, in addition to using resistor, capacitor and inductor, we also use transistor or operation amplifier for signal amplification after filtering. Therefore, noise can be filtered out and the gain can be amplified. However, active filter must use extra bias, which increases the power consumption of the chip itself. In addition, in CMOS process, resistor, capacitor and inductor occupies a too large area, which could easily be interfered by noise. Even the transistor and amplifier also occupy some area. However, in digital filter, software is used for filtering way. It has advantage of small volume and less power consumption. But the disadvantages are, it is not in real time, and it takes some time to display the result. In addition, when digital filter is used, analog to digital conversion needs to be done first, then after the filtering, digital to analog conversion needs to be done again, which could easily lead to the distortion of the signal.
Based on the above factor, it is necessary to develop an attenuator that does not need analog to digital conversion, does not need extra power, of low power consumption, and occupies smaller area.